如何生成给定数据中第23位的CRC值？多种校验方法尝试未果

我需要生成传入数据中第23位的校验值，但尝试使用CRC-8、LRC、BCC及校验和方法计算后，结果均与目标值不符，不清楚需添加或修改什么逻辑才能得到正确的校验值，附上测试代码寻求帮助。

#include <stdio.h>

unsigned char a[19][22] =
{
{0x02,0x01,0x05,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x04}, //ad  (checksum value)
{0x02,0x01,0x05,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x04}, //ad
{0x02,0x01,0x05,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x04}, //ad
{0x02,0x01,0x05,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x05,0x00,0x00,0x00,0x00,0x04}, //b2
{0x02,0x01,0x05,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x04,0x09,0x19,0x53,0x00,0x11,0x20,0x45,0x02,0x91}, //e1
{0x02,0x01,0x05,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x04,0x29,0x20,0x43,0x00,0x11,0x20,0x46,0x03,0x01}, //d3
{0x02,0x01,0x05,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x04,0x38,0x20,0x83,0x00,0x11,0x20,0x47,0x03,0x21}, //da
{0x02,0x01,0x05,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x04,0x43,0x21,0x13,0x00,0x11,0x20,0x47,0x03,0x21}, //d0
{0x02,0x01,0x05,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x04,0x47,0x21,0x23,0x00,0x11,0x20,0x47,0x03,0x21}, //d5
{0x02,0x01,0x05,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x04,0x49,0x21,0x33,0x00,0x11,0x00,0x48,0x03,0x21}, //d7
{0x02,0x01,0x05,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x04,0x51,0x21,0x43,0x00,0x11,0x00,0x48,0x03,0x21}, //d1
{0x02,0x01,0x05,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x04,0x52,0x21,0x53,0x00,0x11,0x30,0x48,0x03,0x21}, //d6
{0x02,0x01,0x05,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x04,0x52,0x21,0x63,0x00,0x11,0x20,0x48,0x03,0x31}, //d7
{0x02,0x01,0x05,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x04,0x52,0x21,0x63,0x00,0x11,0x00,0x48,0x03,0x31}, //d5
{0x02,0x01,0x05,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x04,0x53,0x21,0x53,0x00,0x11,0x20,0x48,0x03,0x21}, //d6
{0x02,0x01,0x05,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x04,0x53,0x21,0x53,0x00,0x11,0x20,0x48,0x03,0x21}, //d6
{0x02,0x01,0x05,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x04,0x53,0x21,0x53,0x00,0x11,0x30,0x48,0x03,0x21}, //d7
{0x02,0x01,0x05,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x04,0x53,0x21,0x53,0x00,0x11,0x20,0x48,0x03,0x21}, //d6
{0x02,0x01,0x05,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x04,0x53,0x21,0x53,0x00,0x11,0x00,0x48,0x03,0x21}  //d4
};


unsigned char calculate_byte_sum(unsigned char *data, int length)
{
    unsigned char checksum = 0;
    int i;

    for (i = 0; i< length; i++) 
    {
        checksum += data[i];
    }
    return checksum;
}

unsigned char calculate_crc8(unsigned char *data, int length) 
{
    unsigned char crc = 0x00; 
    unsigned char polynomial = 0x07;

    for (int i = 0; i < length; i++) 
    {
        crc += data[i];
        for (int j = 0; j < 8; j++) 
        {
            if (crc & 0x80) 
            {
                crc = (crc << 1) ^ polynomial;
            } 
            else
            {
                crc <<= 1;
            }
        }
    }
    return crc;
}


unsigned char calculate_bcc(unsigned char *data, int length)
{
    unsigned char bcc = 0;
    for (int i = 0; i < length; i++) 
    {
        bcc ^= data[i];
    }
    return bcc;
}

unsigned char calculate_lrc(unsigned char *data, int length) 
{
    unsigned char lrc = 0;
    for (int i = 0; i < length; i++) 
    {
        lrc += data[i];
    }
    return (unsigned char)((~lrc));
}


void fcs_test(unsigned char* data, unsigned int len) 
{
    unsigned char ch,ch1, ch2,ch3,ch4,ch5;
    ch = calculate_byte_sum(data, len);
    ch1 = calculate_crc8(data, len);
    ch2 = calculate_bcc(data,len);
    ch3= calculate_lrc(data,len);

    printf("calculate_byte_sum = %02x     calculate_crc8 = %02x    calculate_bcc = %02x    calculate_lrc = %02x\n", ch,ch1,ch2,ch3);
//    printf("fcs = %02x \n", ch);
}


int main()
{
    unsigned int  i;
    for (i=0 ; i < 19; i++)
    {
        fcs_test(&a[i][0], 22);
    }
    return 0;
}

问题排查与修正方案 #

1. 核心错误：校验范围错误 #

你当前代码是对全部22个字节计算校验值，但目标校验位是第23位，说明校验值应该基于前21个字节计算，数组的第22位是已经给出的目标校验值，不能包含在计算范围内。

2. CRC-8实现逻辑错误 #

标准CRC-8的计算是将当前数据字节与CRC寄存器异或，而非相加。你的代码中crc += data[i];是错误的，正确逻辑应改为异或操作。

3. LRC实现不完整 #

标准LRC通常要求取反后加1（即补码形式），而非单纯取反，部分通信协议会明确要求这一步。

修正后的代码示例 #

#include <stdio.h>

unsigned char a[19][22] =
{
{0x02,0x01,0x05,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x04}, //ad  (checksum value)
{0x02,0x01,0x05,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x04}, //ad
{0x02,0x01,0x05,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x04}, //ad
{0x02,0x01,0x05,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x05,0x00,0x00,0x00,0x00,0x04}, //b2
{0x02,0x01,0x05,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x04,0x09,0x19,0x53,0x00,0x11,0x20,0x45,0x02,0x91}, //e1
{0x02,0x01,0x05,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x04,0x29,0x20,0x43,0x00,0x11,0x20,0x46,0x03,0x01}, //d3
{0x02,0x01,0x05,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x04,0x38,0x20,0x83,0x00,0x11,0x20,0x47,0x03,0x21}, //da
{0x02,0x01,0x05,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x04,0x43,0x21,0x13,0x00,0x11,0x20,0x47,0x03,0x21}, //d0
{0x02,0x01,0x05,0x40,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x04,0x47,0x21,0x23,0x00,0x11,0x20,0x47,0x03,0x2